The present invention relates to data caching. More particularly, the present invention relates to apparatus for caching streaming media and to methods of operation of streaming media caches.
Typical file caching methods include a cache receiving a file from a file server, and storing the entire file. Later, when a client desires the file, instead of serving the file from the file server, the file is served from the cache. Because the cache is typically a server that is closer to the client or has higher bandwidth than the file server, the file is served to the client quickly from the cache.
It has been discovered by the inventors, that attempting to apply typical file caching methods to files that include streaming media data, raises many new problems. For instance, serving a streaming media data file from a cache requires much more processing by the cache than with classical file transfers over the web. For example, during normal playback, the cache may need to perform a lot of processing such as packet modification, resequencing, and retiming. As another example, the cache may be called upon to perform random access within the streaming media data file as a result of a client “rewind” or “fast forward” operation. Because, classical caching is typically file-based, such a random access would involve moving within a very large data file.
Another drawback is that since streaming media data files are very large, a huge penalty is incurred if the streaming media data file is deleted. Typically if a file cache determines that it needs more disk space for new files, it will first delete older files, regardless of the size. As an example, if an older file is a streaming media data file that stores an hour-long program, the entire hour-long program is deleted even if the cache only needs to free up the equivalent of 1 minute of space.
Another drawback is that many different streaming media formats exist, each with its own specific streaming requirements. This is in contrast to classical file transfer over the web, where the files are essentially opaque to the cache and for streaming data to clients, the cache does not need to process the actual contents of the file beyond storage and retrieval.
Thus what is required are improved methods and apparatus for storing and serving streaming media within a cache. Further, what is required are methods and apparatus for providing such solutions in economical ways.